5.2.2 Layout interfaces

The HTML page that we found in the previous section describes the layout object called Fingering. Such an object is a symbol within the score. It has properties that store numbers (like thicknesses and directions), but also pointers to related objects. A layout object is also called a Grob, which is short for Graphical Object. For more details about Grobs, see grob-interface.

The page for Fingering lists the definitions for the Fingering object. For example, the page says

padding (dimension, in staff space):

0.5

which means that the number will be kept at a distance of at least 0.5 of the note head.

Each layout object may have several functions as a notational or typographical element. For example, the Fingering object has the following aspects

• Its size is independent of the horizontal spacing, unlike slurs or beams.
• It is a piece of text. Granted, it is usually a very short text.
• That piece of text is typeset with a font, unlike slurs or beams.
• Horizontally, the center of the symbol should be aligned to the center of the note head.
• Vertically, the symbol is placed next to the note and the staff.
• The vertical position is also coordinated with other superscript and subscript symbols.

Each of these aspects is captured in so-called interfaces, which are listed on the Fingering page at the bottom

This object supports the following interfaces: item-interface, self-alignment-interface, side-position-interface, text-interface, text-script-interface, font-interface, finger-interface, and grob-interface.

Clicking any of the links will take you to the page of the respective object interface. Each interface has a number of properties. Some of them are not user-serviceable (‘Internal properties’), but others can be modified.

We have been talking of the Fingering object, but actually it does not amount to much. The initialization file (see Other sources of information) scm/define-grobs.scm shows the soul of the ‘object’,

(Fingering
  . ((padding . 0.5)
     (avoid-slur . around)
     (slur-padding . 0.2)
     (staff-padding . 0.5)
     (self-alignment-X . 0)
     (self-alignment-Y . 0)
     (script-priority . 100)
     (stencil . ,ly:text-interface::print)
     (direction . ,ly:script-interface::calc-direction)
     (font-encoding . fetaText)
     (font-size . -5) 		; don't overlap when next to heads.
     (meta . ((class . Item)
     (interfaces . (finger-interface
                    font-interface
                    text-script-interface
                    text-interface
                    side-position-interface
                    self-alignment-interface
                    item-interface))))))

As you can see, the Fingering object is nothing more than a bunch of variable settings, and the web page in the Internals Reference is directly generated from this definition.